What is the genetic fallacy?

Judging a claim as true or false based purely on where it came from — its origin or source — rather than on its actual merits.

The pattern: the origin of a claim is presented, and that origin alone is taken to establish (or discredit) the claim. It fails because a claim's source is separate from its truth — a good idea from a disreputable origin is still a good idea, and vice versa.

"That safety concern came from a tabloid, so it's obviously rubbish."

The tabloid being a poor source is a reason to double-check, but not in itself a reason to dismiss the specific concern — it has to be evaluated on its own evidence. (Where the claim came from can be relevant — e.g. a reliable expert in their field — but origin alone never settles truth.)

Tip: "Consider the source" is good advice for deciding how carefully to verify, but it's a fallacy when used to replace verification.